A coherent userland (not without occasional warts, but without stuff being deliberately, maliciously ignored, broken or replaced to foster someone's agenda).
ZFS as a first class citizen, without wondering if Oracle will show up and take the ball away.
Jails, although that's not super relevant to the desktop experience.
I won't mention systemd, although I truly dislike it (though I have no particular attachment to init scripts, I was quite fond of Solaris' SMF for example).
The absence of snap and whatever horrors Canonical keeps pushing is another plus, but I'm in not in a good position to judge its impact as I'm blissfully ignorant of how bad they are, I just stumble in the occasional horror story.
Biggest thing I'm missing and wish I had: Docker. Jails may be technically better, but the world went another way and they have no functional ecosystem.